The laboratory mouse is a key model for the study of human diseases mainly because the mouse and human genomes are strikingly similar. The ability to modify the mouse genome by disrupting genes or inserting human genes allows researchers to develop highly specific strains for study and has led to an exponential growth in the number and complexity of strains. Creating these strains is not trivial and complex strains must be kept homozygous through breeding closely related animals;otherwise, non-linked loci will segregate among the offspring and strain characteristics will be disrupted. Cryopreservation is used to store strains that are not actively being studied and to protect strains if the breeding colony is lost. However, during cryopreservation or recovery wild type egg donors are used and the homozygosity of the strain is not maintained. In addition, the available methods to cryopreserve and store strains are expensive, time consuming, and require many animals. There is a pressing need to develop a method for cryopreserving strains in a manner which retains the original genotype. The method must be quick, economic, and use few animals. A combination of routine and novel assisted reproductive technologies will be developed to archive and recover homozygous strains. These processes will use 3-5 times fewer resources compared to current embryo cryopreservation methods. Homozygous strains will be archived by cryopreserving both sperm and ovaries. Strains will then be reconstituted using a combination of surgical artificial insemination (surgical AI) and ovarian transplant. Additionally, serial ovarian transplant and surgical oocyte retrieval methods will be explored as alternative methods to recover cryopreserved sperm and ovaries. The reconstitution of strains from the freezer will be developed to reflect the diverse needs of the scientific community and will provide: i) a fast and low cost recovery, delivering 2-3 homozygous breeding pairs, and ii) a moderately fast, higher cost recovery, delivering =10 homozygous breeding pairs. PUBLIC HEALTH RELEVANCE (provided by applicant): Assisted Reproductive Technologies now account for more than 5% of all births in the first world countries. A major limitation to human IVF is the paucity of oocytes. Our research will help understand and, hopefully, increase the oocytes productivity in humans.